Cooling of a battery is directly related with stable charge/discharge functions and life of the battery. Cooling methods of a battery may be classified into a direct cooling method and an indirect cooling method. A direct cooling method includes forming a flow path through which a coolant flows and allowing the formed cooling flow path to cool a battery cell directly. An indirect cooling method includes allowing a heat conductive member to be in contact with a battery cell without any flow path and cooling the battery cell indirectly through the heat conduction of the heat conductive member.
FIG. 1 and FIG. 2 show the conventional battery pack.
Referring to FIG. 1a and FIG. 1b, the battery pack 100 using a direct cooling method forms a hexahedron. For convenience of description, the hexahedron has surface or side {circle around (1)} as the top surface having a lead 103 of a battery cell 102, surface {circle around (2)} as the bottom surface opposite to surface {circle around (1)} and having a pack level cooling system 104, surface {circle around (3)} and surface {circle around (4)} as the surfaces positioned in the battery stacking direction, and surface {circle around (5)} and surface {circle around (6)} as the remaining edge surfaces.
In the battery pack 100, a cooling plate 101 having a cooling pipe is positioned between the bodies of the battery cell 102, and the cooling plate 101 cools the battery cell 102. When the cooling plate 101 is positioned in every gap between the adjacent battery cells 102, at most four cooling plates may be positioned among three battery cells 102 as follows: cooling plate 1+battery 1+cooling plate 2+battery 2+cooling plate 3+battery 3+cooling plate 4. Surface {circle around (1)}, which is the top surface of the battery pack 100, has an electrode lead 103 positioned thereon and is covered with a lid at the upper part thereof. Surface {circle around (2)}, which is the bottom surface of the battery pack 100, has a pack level cooling system 104 positioned thereon to supply a coolant (cooling water) upwardly to the cooling plate 101.
Herein, since the pack level cooling system 104 is positioned on surface {circle around (2)}, which is opposite to surface {circle around (1)} having the lead 103, it can be applied merely to a uni-directional cell and cannot be applied to a bi-directional cell. The cooling structure of such a system 104 merely applicable to a uni-directional cell is limited, and thus a degree of freedom in designing a pack/module of a battery is decreased.
Referring to FIG. 2, a battery is expanded due to swelling during the operation thereof. Then, cell swelling directions are formed toward surface {circle around (3)} and surface {circle around (4)}. Herein, when the cooling plate 101 is fixed to the pack level cooling system 104 on surface {circle around (2)} at the bottom, the top of the plate 101 is spaced along the swelling directions of surface {circle around (3)} and surface {circle around (4)}. After that, leakage of a coolant occurs on surface {circle around (2)}, where the bottom plate 101 and the system 104 are coupled with each other, due to the spacing of the top of the plate 101 caused by cell swelling. Such leakage of a coolant causes degradation of the life of a battery and a failure in operation of a battery, and thus adversely affects devices (e.g. electric vehicles) to which electric power is supplied from the battery.